Both are good products and I am providing some more information about this below:

Advantage

For the prevention and treatment of flea infestations on cats and dogs, and for the treatment of biting lice (Trichodectes canis) on dogs.

For the treatment of flea infestations on pet rabbits.

Fleas are killed within one day following treatment. One treatment prevents further flea infestation on dogs for up to four weeks, three to four weeks on cats and up to one week on pet rabbits. The product can be used as part of a treatment strategy for flea allergy dermatitis in the cat and the dog. The treatment should be repeated after 4 weeks.

Administration to the Cat

Part the hair on the pet’s neck at the base of the skull until the skin is visible. Place the tip of the pipette on the skin and squeeze firmly several times to empty the contents directly onto the skin

Further information

Imidacloprid is an ectoparasiticide belonging to a group of chloronicotinyl compounds. Chemically, it is more accurately described as a chloronicotinyl nitroguanidine.

Imidacloprid has a high affinity for the nicotinergic acetylcholine receptors in the post-synaptic region of the central nervous system (CNS). The ensuing inhibition of cholinergic transmission in insects results in paralysis and death. Due to the weak nature of the interaction with mammalian nicotinergic receptor sites and the postulated poor penetration through the blood/brain barrier in mammals, it has virtually no effect on the mammalian CNS. The minimal pharmacological activity in mammals is supported by safety studies involving systemic administration of sub-lethal doses to rabbits, mice and rats.

Oral studies in the rat show imidacloprid to be absorbed rapidly from the gastro-intestinal tract. Almost complete absorption (95%) occurs within 48 hours. Peak plasma concentrations are observed within 2.5 hours following administration. Tissue distribution is also rapid with the lowest levels recorded in the brain. The active ingredient undergoes extensive metabolism with only 10-16% remaining as parent compound. Almost complete (96%) elimination occurs within 48 hours, approximately 75% being removed by the kidneys and 21% with the faeces

Frontline Plus

To be used against infestations with fleas, ticks and/or biting lice.

- Elimination of fleas (Ctenocephalides spp.) and insecticidal efficacy against new infestations with adult fleas persists for 4 weeks.

- Prevention of the multiplication of fleas by inhibiting the development of eggs (ovicidal activity), larvae and pupae (larvicidal activity) originating from eggs laid by adult fleas for 6 weeks after application.

- Elimination of ticks (Ixodes ricinus, Dermacentor variabilis, Rhipicephalus sanguineus). The product has a persistent acaricidal efficacy for up to 2 weeks against ticks (based on experimental data).

- Elimination of biting lice (Felicola subrostratus).

Further information

The product is an insecticidal and acaricidal solution for topical use, containing an adulticidal active ingredient, fipronil, in combination with an ovicidal and larvicidal active ingredient, (S)-methoprene.

Fipronil is an insecticide and acaricide belonging to the phenylpyrazole family. It acts by interacting with ligand-gated chloride channels, in particular those gated by the neurotransmitter gamma-aminobutyric acid (GABA), thereby blocking pre- and post-synaptic transfer of chloride ions across cell membranes. This results in uncontrolled activity of the central nervous system and death of insects or acarines. Fipronil kills fleas within 24 hours, ticks (Dermacentor variabilis, Rhipicephalus sanguineus, Ixodes scapularis, Ixodes ricinus, Haemaphysalis longicornis, Haemaphysalis flava, Haemaphysalis campanulata) and lice within 48 hours post-exposure.

(S)-Methoprene is an insect growth regulator (IGR) of the class of compounds known as juvenile hormone analogues that inhibit the development of immature stages of insects. This compound mimics the action of juvenile hormone and causes impaired development and death of the developing stages of fleas. The on-animal ovicidal activity of (S)-methoprene results from either direct penetration of the eggshell of newly laid eggs or from absorption through the cuticle of the adult fleas. (S)-methoprene is also effective in preventing flea larvae and pupae from developing, which prevents contamination of the environment of treated animals with the immature stages of fleas.

Both (S)-methoprene and fipronil are well-distributed in the haircoat of cats within 24 hours after application. The concentrations of fipronil and (S)-methoprene in the haircoat decrease with time and are detectable for at least 59 days after dosing. Parasites are killed through contact rather than by systemic exposure.

No pharmacological interaction between fipronil and (S)-methoprene was noted.